Lipids are an essential part of the diet and metabolism of humans and animals. Although there exist a number of potentially desirable reasons for developing novel methods of delivering lipids to humans, in the field of animal nutrition a rather intense need exists to supply lipids as part of animal feed rations. Specifically, the desirability of lipids stems from their efficient supply of energy density in animal feeds. With the growth of programmed feeding for large numbers of specific types of animals, difficulty has arisen in supplying appropriate types and amounts of lipids. For example, adding certain types of lipids to the diets of dairy cattle significantly enhances their milk production, and other animals exhibit similar growth and health enhancement when the lipid content of their diets is increased.
The term "lipid" refers to fats and fat-derived materials, among other compounds. It includes substances which are relatively insoluble in water, but soluble in typical organic solvents; which are actually or potentially related to fatty acid esters, fatty alcohols, sterols, waxes and the like; and which are utilizable by animal organisms. Lipids are one of the chief components of living cells. Accordingly, as used herein, the term lipid can include various fats, fatty acids, fatty esters, and oils.
A number of such compounds which are unappetizing or inappropriate for use in foods intended for human consumption are nevertheless quite satisfactory and desirable for use as part of animal diets. Such lipids can include the used oils and fats from various cooking processes, such as that referred to as "yellow grease", tallow, poultry oils, fish oils, other animal by-products, as well as oils of vegetable origin.
Although desirable for use in animal feed rations, many of these materials are "low-titer" lipids, meaning generally that they are either semi-solid or liquid at ambient temperatures. Typically, lipid compounds which are referred to as fats are generally solid at ambient temperatures and those which are referred to as oils are generally liquid under the same conditions. As used herein, the phrase "ambient temperatures", is used in its common meaning, for which the term "room temperature" may also be used, to refer to temperatures of between about 20.degree. and 25.degree. Celsius, or 68.degree.-77.degree. Fahrenheit.
Accordingly, any system for including such desirable lipids in the diet of animals has heretofore required some system for transporting, distributing, mixing, and feeding liquids or semi-solid materials. As might be expected, the liquid or semi-solid nature of these materials raises a number of difficulties. For example, distributing liquid or semi-solid materials to animals can be quite difficult compared to distributing dry ingredients given the relatively high viscosities of such materials.
Additionally, when mixed with grains and similar dry feed products, the temperature sensitive lipids also tend to clump, solidify, or otherwise agglomerate, and to disperse nonuniformly through the feed products with which they are mixed.
The nutritional value of lipids to animals and the aforementioned difficulties in handling lipids have led the feed industry to significant expenditures of time and money in attempts to develop systems suitable for mass distribution of lipids in foods or as food supplements.
Previous techniques have included using edible, absorbent host carriers, e.g. grain products, to add lipids to animal feeds. Although this does represent one method of delivering lipids, certain problems remain. For example, the carrier material will very likely be suitable only for certain animal species. The problems of stability, rancidity and handling tend to remain. Often, the carrier tends to comprise well over fifty percent of the weight and bulk of any resulting food product, limiting the amount of lipid that can be included and increasing the cost of distribution of the material.
Other delivery techniques have included forming lipids into powders, an example being the typical dry artificial creamer for hot beverages such as coffee. More recent developments have included encapsulating lipids in a shell formed from a protein and aldehyde complex. These particles have, however, failed to gain commercial acceptance, one reason being that the aldehyde constituents tend to be known carcinogens, and the resulting products cannot be approved for use as animal feed supplements. Other delivery techniques carry lipids in gelatin-type products which rely on the interaction of alginates with various metal salts to produce soft-gelled products.
Nevertheless, despite the efforts of a large number of researchers over a prolonged period of time, there remained no simple, economical system for delivering a lipid, either per se or in extremely high lipid concentration particles, in integral, stable, solid, and highly concentrated form.
Recently, however, and as disclosed in co-pending application Ser. No. 609,541; to James P. Cox; "Lipid Pelletization Methods, Apparatus and Products"; filed Nov. 29, 1983 and assigned to the assignee of the present invention, there has been disclosed a method of forming integral, firm, solid, "dry" pellets or particles of lipids per se containing up to 95 percent or higher lipid concentrations, less water of hydration.
The process disclosed by Cox results in a solid pellet or particle which is integral, generally solid, and contains lipid throughout its entire structure. The pellets are stable over the temperature ranges required for handling and distribution in agricultural situations and unlike any previous lipid delivery system, the pellets can be bagged for storage and transportation with relatively long shelf life and attendant convenience to the end users.
In the Cox process, the pelletized lipids are prepared according to the following scheme: (1) a suitable mixture of water and alginate is formed and then, if necessary, heated to a temperature above which the particular lipid to be included exists in a liquid phase; (2) the liquid or liquified lipid is added to the aqueous mixture of the alginate to form a alginate-water-lipid emulsion; (3) the emulsion is thereafter extruded or otherwise deposited in discrete amounts into a metal salt bath, usually an aqueous solution of calcium chloride (CaCl.sub.2). The calcium chloride sets the emulsion in the configuration in which it was extruded; and (4) the resulting pellet is maintained in the metal salt bath for a sufficient length of time to ensure a desired firmness of the product, after which the particles may be dried, packaged, or mixed with other feed materials as desired.
As suitable proportions, Cox suggests mixing water, alginate and yellow grease into an emulsion containing about 57% water, about 41% yellow grease, and about 0.5% alginate, all by weight, with the remainder being additional emulsifying agents or such as "ammonia (NH.sub.3)" or a "coagulant expander" such as bentonite. This mixture is extruded into a one percent (1%) solution of calcium chloride and allowed to remain for approximately 10 minutes. The resulting pellets are spread out to dry under ambient conditions for 24 hours, after which they exhibit a moisture content of about 30%.
Although the Cox process results in a pellet which contains predominantly lipids and which demonstrates the potential for delivering such pellets as a part of an animal feed ration, mixing the characteristically hydroscopic alginate directly with water results in a gel-like mixture which is difficult to handle efficiently, even if ultimately useful. As a result, the process has generally been difficult to master on a production level basis.
As a first difficulty, alginates are extremely hydroscopic and forming the initial mixture of water and alginate in the manner described by Cox tends to be rather difficult. The water and the alginate mixture becomes extremely viscous and hard to handle. Second, mixing the high viscosity water-alginate mixture with a lipid to form the emulsion necessary to the process can be quite difficult.
Furthermore, the gel-like, viscous nature of the water-alginate mixture makes it difficult to form homogeneous mixtures with larger proportional amounts of lipid. Therefore, from a practical standpoint, forming an emulsion which carries a high enough proportion of lipid to form a resulting pellet carrying a correspondingly high proportion of lipid to quite difficult using the Cox process.
Accordingly, the order of operations called for by Cox tend to be rather time-consuming, difficult, and proportionally limiting, making them more problematic to use on a production scale.
Secondly, the techniques set forth by Cox for drying the pellets have presented difficulty on a production level basis. Absent appropriate drying (other than water of hydration), "watery" pellets present many of the storage and handling problems that liquid or semi-solid lipids presented in the first place.
More specifically, although the various processes discussed in Cox's application refer to "dry" pellets, it should be understood that the production of dry pellets as discussed therein tends to proceed in two stages: first, the production of a "hardened" discrete portion of emulsion--e.g. a pellet--which can be described as "dry" in that any lipids present are no longer in a liquid state. Second, the production of a pellet from which some additional amount of water has been removed and which is "dry" or "drier" or "dried" in that it carries a smaller precentage of moisture.
The Cox disclosure generally discusses several methods of accomplishing the process of removing additional water from such pellets: a rotatable drying cylinder operated under ordinary atmospheric conditions; "conventional" methods of heating the pellets or heating the pellets with a "low, very dry and/or pulsating heat." Alternatively, Cox suggests that any active drying step may simply be unnecessary, or that the pellets will give up water in the presence of admixed grain products, which are generally initially drier than the pellets.
In production quantities and under production conditions, however, it has now been determined that active removal of some water content from the hardened pellets is almost always at least desirable, and often necessary to produce a satisfactory marketable pellet. Additionally, the mere exposure of the pellets to air, either with or without mechanical agitation results in unsatisfactory drying at production levels. Furthermore, conventional active heating techniques undesirably destabilize the pellets unless a significant amount of moisture has first been removed through some other technique. Finally, the amount of moisture which will migrate from the pellets to an admixed grain is not satisfactory for drying just-hardened pellets.
Accordingly, it is an object of the present invention to provide an improved method for forming lipids into stable pellets or particles.
It is another object of the invention to provide improved techniques for drying pelletized lipids, especially those formed according to the present invention.
The foregoing and other objects, advantages and features of the invention and the manner in which the same are accomplished will become more readily apparent upon consideration of the detailed description of the invention, which sets forth preferred and exemplary embodiments.